1. Field of the Invention
The invention relates to a method for controlling the moisture profile of a paper or board web processed on a heated multi-roll calender to optimize the qualities of the paper or board, especially gloss.
2. Description of Related Art
For controlling the gloss of a paper web, a gloss controller is known, the operating principle of which is as follows:                the gloss of the paper web is measured        if the gloss is insufficient, steam is added        steam is added until the gloss is as desired.        
This type of gloss controller for a paper web moisturized on its surface cannot be used in connection with heated multi-roll calendars for the following reasons:                the derivative of the response function of steam changes from positive to negative at a certain steam level. That is, the response resembles a downwards opening second-order polynomial. In other words, following the addition of a certain amount of steam, the addition of steam in fact deteriorates the gloss of the paper web compared with the optimum amount of steam.        when gradient calendering in practical conditions, the body moisture and surface moisture of the paper vary. The response of steam is very dependent on the amount of the surface moisture.        
The reason for the form of the steam response and the violent effect of moisture are the moisture gradients appearing in the direction of thickness of the paper. In an on-line process, and especially in gradient calendering, these are much greater than in conventional calendering. The appearance of gradients is also affected by higher than conventional process heats.